The field of the disclosure relates generally to a housing for a blower system, and more specifically, to a housing for a blower system having surface structures that enhance blower system efficiency and reduce blower system noise.
Centrifugal blower or fan systems are commonly used in the automotive, air handling, and ventilation industries for directing large volumes of forced air, over a wide range of pressures, through a variety of air conditioning components. In some known centrifugal blower systems, air is drawn into a housing through one or more inlet openings by a rotating wheel. The rotating wheel forces the air around the housing and out an outlet end. Some known centrifugal blower systems generate a high speed airflow that produces undesirable acoustic noise. Acoustic noise is generally made up from a combination of mechanical noise and aero-acoustic noise.
In general, mechanical noise is generated from the vibration of moving parts such as the blower or fan motor. Aero-acoustic noise is generated from the mixing or turbulent airflow and the airflow across the surfaces of the blower housing and ducts. Aero-acoustic noise can include whistling, tonal noise, or broadband noise generated by interactions within the airflow and noise generated as the air travels through the blower housing. This noise can be caused by the disruption of the airflow, which can interact with various system components to generate the noise. In addition, this noise may be caused by pressure changes within the airflow generated by portions of the airflow at different pressures interacting with each other or with portions of the blower housing. These pressure variances may be caused by non-uniform flow, adverse flow structures generated in the airflow, or airflow recirculation.
In some known blower systems, airflow recirculation may be caused by the mixing of the airflow entering the blower in an axial direction parallel to the rotation axis of the rotating wheel and the airflow within the blower flowing in a radial direction perpendicular to the rotation axis. The recirculating airflow generally has a swirling component that generates adverse flow structures, such as eddies or vortices, within the airflow. In addition, a laminar boundary layer of the airflow along the blower housing surfaces facilitates flow separation and can lead to the generation of these adverse flow structures or flow separation. These adverse flow structures can cause non-uniform airflow within the blower housing and at the blower outlet, which generates undesirable noise and facilitates inefficient operation of the centrifugal blower system.
The boundary layer is a very thin layer of air lying along the surfaces of the blower housing that follows the surfaces. As the air flows along the surfaces, air in the boundary layer flows smoothly over the smooth housing surfaces generating a laminar flow layer. As the air continues to flow further along the surfaces of the housing, the thickness of this laminar flow boundary layer increases due to friction with the surfaces, and in some instances, the boundary layer may also separate from the surfaces. This can result in the generation of large scale adverse flow structures, and also the airflow near the surface becoming detached, for example, curved surfaces such as the inlet ring of the blower housing. At some distance along the surface of the curved inlet ring, airflow separation may occur. This airflow separation can be reduced or eliminated with the generation of a turbulent boundary layer.
Generally, as the boundary layer height increases and interacts with the surrounding flow, it can alter the proximate full flow profile or velocity distribution of the flow. For example, in a duct, the boundary layer perturbs the flow from the walls and changes the full flow distribution and a fully developed flow profile develops. If the airflow is viscous enough or the velocity is low enough, the airflow can remain laminar. However, if the airflow is not viscous enough or the velocity is too high, the friction at the surface can actually cause some flow reversal, i.e. eddies and vortices, which start a transition to a fully turbulent flow. Placing upstream surface perturbations in the airflow can facilitate generating eddies and vortices in the airflow, which can interact with and break up the large adverse flow structures and facilitate developing a fully developed turbulent flow sooner.